1. Field of the Invention
The present invention relates to a method and apparatus for determining a condition for performing a write operation on an optical disc that is specially designed to perform a write operation thereon at high speeds.
2. Description of the Related Art
Examples of optical discs, from/on which data can be read and/or written optically, include write-once discs such as CD-Rs, DVD-Rs and BD-Rs to which data can be just added and rewritable discs such as DVD-RWs, DVD-RAMs and BD-REs on which data stored is rewritable. For any of these various types of optical discs, a standard writing speed is defined. Specifically, such a writing speed is represented by either a linear velocity or a transfer rate. In this description, the writing speed will be represented by the linear velocity in most cases.
At an increasing demand in the market and thanks to the development of technologies, the highest writing speed on optical discs has been rising these days. And a 16× write operation has already been realized for DVD-Rs as a result. As for BD-Rs, discs and recorders that achieve 4× recording are now under development. As used herein, the “**x” means that the highest writing speed is ** times as high as the standard writing speed.
To increase the writing speed, the recorder needs to not only rotate a given optical disc at higher velocities but also increase the recording power of a laser beam pulse to be applied during the write operation and the signal modulation rate as well. Also, before a write operation is actually performed at such a high speed, the best writing conditions for that writing speed are normally determined by performing a tentative write operation (which will be referred to herein as a “test write operation”) on the given optical disc. That is why on an optical disc, areas for performing such a test write operation are provided inside and outside of the user data storage area of the optical disc.
FIG. 4 schematically illustrates a normal track layout for an optical disc 100. As shown in FIG. 4, the optical disc 100 has user data tracks 102 to write user data thereon, an inner test track 101 arranged inside of the user data tracks 102, and an outer test track 103 arranged outside of the user data tracks 102. Data can be either just added once, or rewritten a number of times, on the inner and outer test tracks 101 and 103 and the test write operation is performed on these tracks to determine the data writing conditions.
For example, Japanese Patent Application Laid-Open Publication No. 2002-352430 discloses a conventional method and apparatus for determining conditions for a high-speed write operation. More specifically, that patent document discloses a method for determining the best writing conditions for the writing speed on user data tracks based on results of test write operations that have been performed at multiple different writing speeds on the outer area of the optical disc. The document also discloses a method of correcting the dependence on a radial location on the disc by making an interpolation based on results of test write operations on the inner and outer areas.
If a high-speed write operation is performed on a normal optical disc with a thickness of 1.2 mm and a diameter of 12 cm, the optical disc is preferably used at a rotational velocity of approximately 10,000 rpm or less, considering the maximum rotation performance of the spindle motor, noise, and precaution against possible rupture of the disc. Also, if the optical disc is rotated at a constant rotational velocity, the write linear velocity on the innermost area with the smallest radius is lower than the one on the outermost area with the largest radius. For that reason, if a test write operation is performed on the inner test track with the smallest radius, it is difficult to perform the test write operation at a high speed due to the limit of the rotational velocity. More specifically, on a BD, for example, if the writing speed is 5×, the rotational velocity in the vicinity of the innermost radius of 22 mm reaches as high as approximately 10,000 rpm. That is to say, the rotational velocity on the inner test track becomes too high to perform a test write operation on it easily at a speed of 6× or even higher speeds.
According to the method disclosed in Japanese Patent Application Laid-Open Publication No. 2002-352430, the outer test track that enables a high-speed write operation is used for test writing. And such a method is effective only when the rotational velocity is relatively low. It is also effective if the distribution of write properties from the innermost area of the disc through the outermost area thereof is already known. However, if the relation between the write property on the outer test track and the one on the inner test track or the user data tracks were an unexpected one, writing conditions that could result in greater errors could be obtained unintentionally.
An example of such an awkward situation will be described with reference to FIGS. 5A and 5B, which show how the best recording power changes according to the radial location of a write track in a situation where the writing speed on a certain optical disc is set to be constant. Ideally, the best recording power on an optical disc should be constant irrespective of the radial location. Actually, however, a real optical disc has some property varying according to the radial location. For example, the thickness of the recording film thereof may increase monotonically in the radial direction. In that case, the recording power 1d that has been obtained by making an interpolation between the recording power 1a on the inner test track 101 and the recording power 1b on the outer test track 103 agrees with the actual recording power 1c on the user data tracks 102 as shown in FIG. 5A.
However, the write property could vary distinctly on the outer area of an optical disc, for example. More specifically, the coating layer or the recording film could become extremely thin around the outermost area of a disc. In that case, the recording power 2d that has been obtained by making an interpolation between the recording power 2a on the inner test track 101 and the recording power 2b on the outer test track 103 would disagree with the actual recording power 2c on the user data tracks 102 as shown in FIG. 5B, which is a problem.
Such a problem arises because the conventional method is based on a supposition that any variation occurring on an optical disc in the radial direction should be able to be approximated linearly, for example. That is why if a property of an optical disc varied distinctly on the outer test track 103, then the property on the user data tracks 102 would be unpredictable even by performing a test write operation on the outer test track 103. For that reason, if data is going to be added to an optical disc on which another set of data has already been written through a middle portion of the user data tracks 102, then the conditions for such a write operation to be started at the middle portion cannot be determined properly. That is to say, according to the method of Japanese Patent Application Laid-Open Publication No. 2002-352430, it is very difficult to predict properly high-speed writing conditions at such a middle portion.
On top of that, since the outer test track 103 of an optical disc is located outside of the user data tracks 102 thereof, no read/write property could be defined for that track 103 in the specification of a product. That is why even an optical disc that has been shipped as a good product may have a different property on the outer test track 103 from the ones on the inner test track 101 and the user data tracks 102. Such a radial distribution of properties on an optical disc may be produced due to a variation during the manufacturing process, for example. And the distribution can also be produced due to a difference in the method of making the recording film. For example, the recording film could be formed by performing either a spin coating process of an organic recording film or a sputtering process of an inorganic recording film on the optical disc.